Blood clots are not what most caregivers worry about after a glioblastoma diagnosis. Yet venous thromboembolism (VTE) - a clot forming in a deep vein or traveling to the lungs - ranks among the most common serious complications during GBM treatment. Understanding why it happens, recognizing it, and knowing how your care team can reduce the risk is practical knowledge that may protect the person you care for.
How common are blood clots in glioblastoma patients?
Between 8 and 39 percent of people with glioblastoma develop venous thromboembolism during treatment. GBM carries one of the highest blood clot rates of any cancer type. Most clots occur within the first 12 months after diagnosis, with many developing in the weeks right after surgery. More than one in five newly diagnosed GBM patients developed a VTE during treatment, with advanced age and prior cancer history as key risk factors.
What is a VTE and what forms does it take?
VTE is a term for two related events. A deep vein thrombosis (DVT) is a clot that forms in a large vein - usually in the leg or pelvis. A pulmonary embolism (PE) occurs when part of that clot breaks free and travels to the lungs, where it can block blood flow and become life-threatening. Both are more common in GBM patients than in most other cancers, and either can develop at any point during treatment, including weeks after surgery.
Why does glioblastoma carry such a high clotting risk?
No single factor explains the high risk. Several biological and treatment-related mechanisms combine to make GBM patients more prone to clotting throughout treatment.
Tumor biology primes the blood to clot
GBM cells produce large amounts of two proteins - tissue factor and podoplanin - that directly activate platelets and the body's clotting cascade. This creates a hypercoagulable state: the blood is constantly ready to clot more readily than normal. IDH-wildtype tumors express these proteins at higher levels than IDH-mutant tumors. This may partly explain why patients with IDH-wildtype GBM face higher VTE rates during treatment.
Surgery and recovery
Brain tumor surgery significantly increases VTE risk. Prolonged anesthesia, bed rest after the operation, and the body's post-surgical inflammatory response all raise clotting risk. Longer operating time, greater blood loss, older age, and conditions like diabetes each independently increased blood clot rates in the weeks after surgery.
Limb weakness caused by the tumor
Many GBM patients develop one-sided weakness or partial paralysis - called hemiparesis - because the tumor disrupts brain pathways that control limb movement. When an arm or leg cannot move normally, blood flow through the deep veins slows significantly. Slower flow means longer contact time between blood and the vein wall, which increases the chance of clot formation. Limb weakness consistently predicts VTE risk in high-grade glioma patients.
Steroids used to reduce brain swelling
Dexamethasone is the steroid most commonly used to reduce swelling around the tumor during GBM treatment - Glioblastoma Brain Edema: Causes and Treatment explains how it works. Corticosteroids like dexamethasone change the balance of clotting proteins in the blood, making it more likely to clot. Extended steroid use contributes to VTE risk in cancer patients, though we are still studying exactly how much this effect matters in GBM.
Extended treatment and reduced activity
The standard Stupp protocol - radiation plus temozolomide for about seven weeks, followed by up to six months of maintenance chemotherapy - requires sustained treatment over many months. During this time, many feel exhausted and rest far more than before diagnosis. When patients stay inactive for long periods, blood pools in leg veins, which leads to DVT. Managing Temozolomide Side Effects During GBM Treatment covers practical strategies for staying safely active through treatment.
What are the warning signs of DVT and pulmonary embolism?
Get help fast when these symptoms appear. Call your care team right away or go directly to an emergency room if you notice any of the following:
- Swelling, redness, or warmth in one leg - especially the calf or inner thigh - that appeared without an obvious injury
- Leg pain or aching with no clear cause
- Sudden shortness of breath or labored breathing
- Chest pain that worsens with a deep breath
- A rapid or irregular heartbeat at rest
- Coughing up blood - call 911 immediately if this happens
- A drop in oxygen levels on a home pulse oximeter that cannot be explained by another known cause
Not all DVTs produce symptoms. Some appear only on a scan ordered for another reason. This is why doctors order regular scans even when the patient seems stable.
How do care teams reduce blood clot risk during GBM treatment?
VTE prevention in GBM usually combines physical and medication-based strategies, typically starting around the time of surgery. A study of 695 GBM patients found that combining enoxaparin (a low molecular weight heparin) with intermittent pneumatic compression had the lowest blood clot rates at 2.6 percent, compared with enoxaparin alone at 8.6 percent and certoparin alone at 6.9 percent. Centers typically use these steps:
- Graduated compression stockings. These apply gentle pressure to the legs to keep blood circulating through the deep veins. Doctors usually fit them before or just after surgery, and patients may wear them throughout the hospital stay and into early recovery at home.
- Intermittent pneumatic compression (IPC) devices. Inflatable cuffs placed around the legs that rhythmically squeeze and release to actively push blood toward the heart. Hospitals commonly use them in the early days after surgery, often along with compression stockings.
- Low molecular weight heparin (LMWH). Injectable blood-thinning drugs that doctors typically start in the days after surgery once bleeding is controlled. Timing and duration depend on the individual patient's bleeding risk.
- Early movement. Getting the patient walking, even short distances in the hospital corridor, as soon as safely possible after surgery. The physiotherapy team guides this carefully, aiming for the earliest safe movement rather than full recovery.
- Good hydration. Adequate fluid intake keeps the blood at a healthy thickness and reduces the tendency to thicken and stagnate in leg veins. This is straightforward but often overlooked during the hospital stay.
When a blood clot is found - treatment decisions in GBM
If VTE develops during GBM treatment, doctors usually prescribe anticoagulation to prevent the clot from growing and to reduce the risk of a new one forming. LMWH has long been the main treatment for cancer-related clots. Direct oral anticoagulants (DOACs) - including rivaroxaban and apixaban - are now being studied in brain tumor patients, with a trial currently assessing the safety and effectiveness of rivaroxaban in glioma patients.
The key challenge is that GBM patients already face high risk of intracranial hemorrhage - bleeding inside the brain - because of the tumor and any recent surgery. The anticoagulants that treat a leg clot also thin the blood more broadly, which can increase this bleeding risk. Doctors must carefully weigh the tumor's location, how recently surgery occurred, signs of micro-bleeding on MRI, and the patient's full medical picture. No single protocol works for all GBM patients - each decision is based on the specific risks and benefits for that person.
If your hospital lacks brain tumor specialists experienced with VTE management, a second opinion from another expert can help. Art of Healing Cancer offers remote consultations using your MRI scans and medical records.
Questions to ask your neuro-oncology team
Have these focused questions ready for clinic appointments to make the most of limited time with the oncologist:
- What is this patient's individual VTE risk level, given the tumor subtype, surgical history, and current mobility?
- When does blood clot prevention start, and which approach - physical, medication-based, or both - is planned?
- Should compression devices be used at home after hospital discharge, and if so, how?
- What symptoms should prompt an emergency call, and what can wait for the next scheduled visit?
- If a clot is diagnosed, which anticoagulant would you recommend, and what are the key risks and benefits in this case?
- Is there an active clinical trial for VTE management in GBM patients that this patient might be eligible for?
Your First 30 Days After a Glioblastoma Diagnosis offers a useful structure for staying organized across all aspects of early care.
When to talk to your doctor
Call the oncology team or go directly to an emergency room if the patient develops sudden leg swelling, chest pain, difficulty breathing, or coughs up blood. Do not wait for a scheduled appointment. If VTE has already been diagnosed and you doubt whether the anticoagulation plan is right for the patient - especially if surgery was recent or if a current scan shows brain bleeding - talk with the neuro-oncologist right away. VTE is manageable in GBM, but catching it early matters because things can get serious quickly.
This article is for general information and is not a substitute for medical advice. Always consult your oncologist or care team about your specific situation.